carbon dioxide—new uses for an old refrigerant

Review

Carbon dioxide—new uses for an old refrigerant

Andy Pearson*

Star Refrigeration Ltd, G46 8JW, Glasgow, UK

Received 5 September 2005; received in revised form 12 September 2005; accepted 13 September 2005

Available online 2 November 2005

Abstract

Carbon dioxide has been used as a refrigerant in vapour compression systems of many types for over 130 years, but it is only

in the last decade that inventive minds and modern techniques have found new ways to exploit the uniquely beneficial properties

of this remarkable substance. This paper traces the development of the old carbon dioxide systems, considers the technical,

commercial and social reasons for their slow development and subsequent decline and examines the recent renaissance across a

surprisingly broad range of applications, from trans-critical car air conditioners to low temperature industrial freezer plants. The

paper then concentrates on industrial refrigeration systems, which were the basis of early developments in the period 1865–

1885, but which have been somewhat overlooked in the current renaissance. The paper concludes with a review of possible

future developments, indicating the areas of research and product development required to maximise the potential of the

only non-toxic, non-flammable, non-ozone-depleting, non-global-warming refrigerant available for Rankine cycle vapour

compression systems in the 21st century.

q 2005 Elsevier Ltd and IIR. All rights reserved.

Keywords: Refrigeration; Air conditioning; History; Review; CO2; Technology; Recommendation; Research

Dioxyde de carbone: nouvelles utilisations d’un vieux frigorigene

Mots cles : Froid ; Conditionnement d’air ; Historique ; Enquete ; CO2 ; Technologie ; Recommandation ; Recherche

1. Introduction

There are five substances generally recognised as

‘natural refrigerants’ in modern refrigeration. Air is used

in a variety of gas cycles, with no change of phase, and can

achieve reasonably low temperatures, but the low theo-

retical efficiency of the Brayton cycle and the difficulty of

getting close to that ideal have limited its use. Water vapour

has been used with large centrifugal and axial turbines in

open systems but the low pressures, large swept volumes

0140-7007/$35.00 q 2005 Elsevier Ltd and IIR. All rights reserved.

doi:10.1016/j.ijrefrig.2005.09.005

* Tel.: C44 141 638 7916; fax: C44 141 638 8111.

E-mail address: [email protected].

and evaporation temperature limit of 0 8C place severe

restrictions on its use and make it fundamentally unsuited to

smaller air conditioning systems and industrial cooling and

freezing applications. Ammonia, carbon dioxide and

hydrocarbons have a broader range of application, and are

used in much more conventional systems. Despite a

generally excellent safety record there is a strict limit on

the allowable charge of hydrocarbon systems, which makes

them unsuitable for use in large water chillers and industrial

systems unless relevant safety standards can be applied. In

many ways ammonia is ideal for large industrial systems

where its mild flammability, pungent smell and low

threshold limit value do not present problems. It is, however,

clearly unsuited to domestic, automotive and small

International Journal of Refrigeration 28 (2005) 1140–1148

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A. Pearson / International Journal of Refrigeration 28 (2005) 1140–1148 1141

commercial refrigeration and heat pump systems. This

leaves carbon dioxide as the only natural refrigerant to find

favour across the broad spectrum of automotive, domestic,

commercial and industrial refrigeration and air-conditioning

systems (Pettersen [11]).

2. Historical perspective—early steps

The first steps towards modern carbon dioxide refriger-

ation systems were taken in the 18th century by two Scots

physicians, Dr William Cullen and Dr James Black. Cullen,

who practiced medicine in Glasgow, was also professor of

medicine at Glasgow University and, in 1748 established the

department of Chemistry in the university. He is credited

with the discovery of latent heat through his experiments

with water in 1755, and also observed that the boiling point

of water could be reduced by lowering the pressure below

atmospheric. This led to experiments with various other

volatile fluids, such as sulphuric ether, although in these

early systems the fluid was exhausted to atmosphere, not

recirculated. Black was one of Cullen’s medical pupils, and

succeeded him as professor of chemistry at Glasgow in

1755. Black’s experiments heating ‘magnesia alba’ (mag-

nesium carbonate) led him to the discovery of carbon

dioxide, which he called ‘fixed air’. Further experiments

proved that this unusual gas was involved in many familiar

processes, including burning and breathing. Black correctly

predicted that ‘fixed air’ would be present in small quantities

in the atmosphere, although it was many years until the level

of 0.03% was confirmed. Neither Cullen nor Black was

primarily interested in thermodynamics or refrigeration, and

their ideas were not developed for nearly a century.

(Thevenot [13]).

Oliver Evans of Delaware proposed a closed cycle for

refrigeration in 1805, although no such systems existed at

that time, and this innovation did not progress until Evans’s

friend Jacob Perkins was granted British Patent number

6662 in 1834 in London for his ethyl ether machine. Perkins,

who was 68 by then, did not exploit his patent, and vapour

compression did not progress until Alexander Twining, a

professor at Yale, patented another ethyl ether-based system

in the USA in 1850. Twining made several efforts to

commercialise his system, including an ice plant installed in

1856 in Cleveland producing 2000 lb (909 kg) in 20 h, but

he did not achieve long term success. At the same time,

James Harrison in Australia developed an ethyl ether based

vapour compression ice machine, probably in complete

ignorance of the work of Perkins and Twining. Harrison

brought his system to London in 1856 to patent and develop

it, and gave several successful demonstrations to notable

scientists of the day, including Michael Faraday and John

Tyndall (Gosney [1]). Although these early systems may

appear to be novelties, they were certainly not trivial.

Twining’s Cleveland plant is said to have had a double

acting compressor with a 210 mm diameter piston and

450 mm stroke. Harrison’s 1857 machine, described in

British Patent number 2362 had a 380 mm bore and a

770 mm stroke.

3. Diverse developments of rival technologies

Faraday’s interest in artificial cooling went back to 1824

when he demonstrated a form of absorption cooling using

ammonia and silver nitrate in a sealed U-tube. He used this

arrangement to demonstrate the liquefaction of several

common gases. Absorption systems using aqua-ammonia

were further developed by Ferdinand Carre in the 1850s and

immediately found widespread success in block ice making.

In 1867 (the year after the civil war ended) there were three

artificial ice plants in San Antonio, out of five in Texas and

only eight in total in North America. Harrison attempted to

be first to ship beef from Australia to England on the sailing

ship Norfolk in 1873. Believing that mechanical equipment

would not be acceptable on board ship, Harrison’s system

used a stock of ice and salt to chill brine, which was trickled

over pre-frozen meat wrapped in heavy waterproof canvas

sacking. This early marine venture failed, apparently

because leaks from the brine circulation system contami-

nated the cargo during the voyage. Harrison might have

been more successful if he had trusted his equipment; in

1876 Charles Tellier of France equipped an old British ship,

the Eboe, with three methyl ether compressors for the first

transatlantic shipment of refrigerated meat. Renamed

‘Frigorifique’ by Tellier, she sailed from Rouen to Buenos

Aires in 105 days with a small cargo of cattle and sheep

carcases, and returned with 25 ton of chilled beef. The

following year Ferdinand Carre equipped the SS Paraguay

with a marine version of his absorption machine, for the

shipment of 150 ton of frozen beef from Marseilles to

Buenos Aires and returned to France with a further 80 ton,

all reportedly ‘edible’ when unloaded in Le Havre [13].

Carre’s method of brine chilling was initially popular for

ice-making installations on shore, and was the basis of

Thomas Mort and Eugene Nicolle’s first proposals for the

shipment of meat to England from Darling Harbour, Sydney

in the 1870s. However, although Nicolle had constructed

several successful absorption ice plants for warehouses in

the Sydney area, he fitted the SS Northam with an air cycle

system in 1876, after permission to use ammonia on board

was refused. Unfortunately, owing to problems during the

commissioning of the system, the Northam sailed for

England without a cargo, and although the plant worked

satisfactorily throughout the voyage, no meat was carried.

Further misfortune followed, when the Northam was lost at

sea during the return voyage in 1877.

Other practitioners also favoured the air cycle, which had

been proposed in 1820 by Richard Trevithick, an employee

of J&E Hall in their pre-refrigeration era (Miller [8]), but

which was not demonstrated in a commercial machine until

25 years later. Dr John Gorrie, a Florida physician,

A. Pearson / International Journal of Refrigeration 28 (2005) 1140–11481142

constructed his ice plant using an air compressor in 1844,

prompted by the lack of ice for treatment of malaria patients

in his infirmary. Alexander Kirk, a Scottish oil engineer,

developed a much more effective air-cycle machine in 1862.

Unlike Gorrie’s ice maker, Kirk used a closed cycle based

on Rev Robert Stirling’s heat engine, and it is reported that

the first machine ran continuously for ten years! Joseph

Coleman, one of Kirk’s colleagues, further developed this

Stirling cycle machine, and in the mid 1870s corresponded

with Lord Kelvin of Glasgow University. Kelvin introduced

Coleman to Henry and James Bell, butchers in Glasgow.

Together they developed the Bell–Coleman air cycle to suit

marine transport, and patented it in 1877. In 1879 they

equipped the SS Circassian for the trans-atlantic run and the

SS Strathleven for the first successful shipment of frozen

meat from Australia to England. These set the pattern for

marine refrigeration systems for the next decade, although

both ships were stripped of their refrigeration plant after

only one voyage.

Paul Giffard in France and Franz Windhausen [14] in

Germany produced refinements of the Gorrie air cycle

design in the 1870s and licenced their technology to

companies on both sides of the Atlantic. J&E Hall of

Dartford, and Alfred Haslam of Derby took licences for air

machines during the late 1870s and supplied the marine

market from 1881 onwards. With a licence from Giffard in

1878, J&E Hall’s young owner, 20 year old Everard Hesketh

started a 10 year air compressor development programme

which turned the company from a ‘languishing, out-of-date’

engineering workshop into a leader in industrial refriger-

ation technology. The Haslam Foundry and Engineering

Company also started their air compressor programme in

1878, and equipped their first meat carrier, SS Orient in

1881, followed by the sailing ship Mataura the following

year. Fig. 1 shows a time-line of some refrigeration

developments. It is evident that, in the period 1845–1885,

there were eight major developments in the choice of

refrigerant or system, but from 1885 to 1925 there were

none. The 40 years of continual effort must have been

prompted, fundamentally, by a deep-seated dissatisfaction

with the ‘state-of-the-art’.

Fig. 1. Timeline of refrigeration development.

4. System rationalisation—the dominance of vapour

compression

A common trait of all types of early refrigeration

equipment was that the concepts outstripped the manufac-

turing capability of the day, and therefore progress was

erratic, because each new development was dependent upon

parallel innovation in related fields. For example, various

compressors were proposed from 1820 onwards, but could

not be commercialised until machining capability had

advanced sufficiently and suitable prime movers were

available. Although the machines he developed in Australia

seemed to work well, James Harrison was severely critical

of the standards of workmanship at that time. Early vapour

compression systems used a variety of naturally occurring

compounds, including ether, ammonia, carbon dioxide and

sulphur dioxide. Each had its own advantages and draw-

backs, and consequently rose and fell in popularity as

technical development opened up new possibilities.

In vapour compression, ethyl ether systems were the first

to be proposed, as early as 1834, perhaps because ether was

readily manufactured, already in use as a solvent and easy to

work with as it is liquid at room temperature and

atmospheric pressure. As ether is highly flammable and

required to operate below atmospheric pressure to create ice,

these systems were never sufficiently safe or reliable to

achieve commercial success, although James Harrison

constructed the first marine system in 1855 in Australia

and persevered with ether until his death in 1893.

Carbon dioxide was the next to make a breakthrough,

through the work of Thaddeus Lowe in Texas. Lowe was a

self-taught scientist with a passion for aeronautics, and was

responsible for founding the Union Army’s Observation

Corps in 1861. Lowe’s compressor was developed in 1860

for filling military observation balloons with hydrogen, and

he served as an observer for the Unionists throughout the

American Civil War. His compressor was adapted for CO2

in 1866 and then used for the manufacture of artificial ice.

Lowe was some 20 years ahead of other developers of

carbon dioxide systems, and it has therefore been suggested

that his systems made ‘dry-ice’ in an open system. However,

there is no doubt that his British Patent, number 952, of 1867

(Newton [9]) discloses a closed vapour compression cycle,

with compressor, condenser and evaporator. In 1869 he was

narrowly defeated by Henry Howard in the race to be the

first to ship frozen beef, by sea, from Texas to New Orleans,

supposedly because Lowe’s custom built refrigerated cargo

ship, the William Tabor, was too large to dock in New

Orleans harbour (Woolrich [15]). Unlike ether, carbon

dioxide was non-flammable, and essentially non-toxic, but

for a closed vapour compression cycle it required extremely

high pressures—much higher than those used in the steam

boiler plant of the day. This perhaps was the cause of the 20

year delay, letting ammonia and sulphur dioxide systems

become established first. Throughout the 1860s ammonia

had been used in absorption systems, but in 1872, the first


ammonia compressor was developed by David Boyle in

Texas, closely followed by Prof Carl von Linde’s machine

in Germany in 1876. In 1874 Raoul Pictet produced a

system in Switzerland based on a sulphur dioxide

compressor, and a few years later, in 1878, methyl chloride

systems were also developed.

Thus the five main refrigerants of the 19th century, ether,

carbon dioxide, ammonia, sulphur dioxide and methyl

chloride were introduced over a 25 years period and vied

with each other and with alternative technologies to

dominate the market. It is evident that ease of use was a

prime factor in system selection, followed to a lesser extent

by reliability, space required, installation cost, efficiency

and safety. All the systems in use were to some extent

hazardous, either because the refrigerant was highly

flammable (various ethers, naphtha, chemogene, methyl

chloride), or noxious (ethers, ammonia, sulphur dioxide) or

required high-pressure equipment (carbon dioxide).

Development tended to progress where there was a strong

commercial demand for refrigeration, and the local balance

of selection factors meant that different systems gained

popularity in different markets. Absorption was popular in

early ice plant because it was simple and relatively easy to

construct, requiring no compressor and no prime mover—

usually a steam engine in the nineteenth century. It lost

popularity because it was unreliable, possibly because

systems were relatively large and because they operated

intermittently, not continuously. Air cycle, like absorption,

was relatively simple and found favour for early marine

installations because the plant was relatively compact. In

systems based on Gorrie’s design there was no need for a

complex and messy brine system as the air could be used in

open systems, drawing from the hold, compressing, cooling

and expanding back into the refrigerated space. The

disadvantage of snow forming in the suction was to an

extent overcome by using suction superheaters and

improved valve designs. Ether was first choice in vapour

compression because it exists as a liquid at room

temperature, but this means that to chill brine or produce

ice the suction pressure is sub-atmospheric. This required

relatively large compressors and led to unreliability,

including the risk of explosions.

By the 1880s the capacity required of installations on

land made efficiency a more important factor in system

selection. Air cycles required 8–10 times the coal required

of an ammonia plant, and absorption systems required 60%

more fuel. In addition, most systems were cooled by river

water, and the absorption system was reckoned to require

two and a half to three times more water than an ammonia

compression plant. Ammonia was still not preferred at sea,

because the noxious smell posed a major hazard in the event

of a leak below decks. For small systems air continued to be

used, and carbon dioxide compressors improved sufficiently

to make them the preferred choice for larger systems. Franz

Windhausen patented an improved carbon dioxide com-

pressor in 1886 and this design was licensed and further

improved by Everard Hesketh of J&E Hall who developed a

compound compressor to improve efficiency of carbon

dioxide systems in 1889. Over the next 6 years Halls

installed over 400 such systems, mainly on ships, although a

few were for dockside cold stores. Space requirements were

obviously important on ships, but less so on land; and the

same could be said for safety. A plant explosion or a major

leak of toxic gas could cause a ship to go down with all

hands. Although there were several disasters on shore with

ammonia plant, most notably the fire in the Columbian

exhibit at the World’s Fair in Chicago in 1893, which caused

17 deaths, owners and designers of plant were rather more

relaxed about safety. Thus land and marine designs

diverged. Ammonia compressors were typically larger, but

being a lower pressure design could be built quite cheaply.

They were generally reliable, and were kept substantially

leak-tight, owing to the nasty smell of ammonia. Carbon

dioxide compressors were much smaller, but of a heavy

construction to contain the pressures of 50 or 60 bar

required. In some cases pressures were even higher,

permitting supercritical operation. Usually the high pressure

was limited to a heavy walled cylinder, and the crankcase

was open, with shaft seals on the piston rod, rather than the

modern, sealed crankcase designs The driver, still usually a

steam engine, was much larger than the compressor.

5. Impediments to progress

It took about a century for refrigeration to progress from

a laboratory curiosity of no commercial value to the basis of

a fledgling industry, and a further 50 years to grow this new

industry into a thriving market. The slow progress is simply

explained by a complete lack of appreciation of the

commercial possibilities for artificial cooling. However,

even when the new technology clearly and easily met a

need, there were still barriers to be overcome. John Gorrie

was a well-respected figure in his local community and had

been mayor of his hometown, Apalachicola, in 1836. When

he built his artificial ice maker in 1844 he was afraid of

adverse comment from the local church leaders, so he did

not publish his remarkable feat. Writing under the pen-name

‘Jenner’ he predicted in the local press that it might be

possible to make ice in such a manner. The New York Globe

duly reported that ‘there is a crank, down in Apalachicola,

Florida, that thinks he can make ice by his machine as good

as God Almighty.’ Dr Gorrie did not attempt to

commercialise his invention until 1851 when his US patent

was published (Thevenot [13]).

Patents could also act as impediments to progress, as

competitors tried to establish themselves in new markets.

J&E Hall and the Haslam company were both embroiled in

legal actions instigated by Bell and Coleman over a patented

method of removing moisture from suction gas in air

compressors. The dispute was only resolved when Haslam

purchased the patent rights from Bell and Coleman, and


Everard Hesketh of Halls designed an alternative moisture

separator (Miller [8]). Both the technical and the

commercial considerations in this type of dispute must

have acted as a major distraction from the development and

testing of these new systems. Much innovative engineering

may have been ‘wasted’ in circumventing existing patent

restrictions rather than developing new concepts.

Lack of commercial ability may also have restricted

progress in artificial cooling, as many of the innovators were

unschooled mechanics from a rural background or pro-

fessionals from medicine, academia, publishing, and even

theology. Dr Gorrie was unfortunate because when he

finally agreed to develop his icemaker, his principal backer,

a Boston businessman died within a few months. The project

never recovered, and Gorrie himself died a few years later in

1855. It is notable that David Boyle, producer of the first

ammonia compressor only produced 20 compressors a year

and went out of business after 10 years. The company

formed by Prof Linde 4 years after Boyle’s produced over

750 compressors for breweries alone in the first 15 years of

its existence (Hard [2]), and it is still a major player in the

refrigeration and process gas markets worldwide nearly 130

years later. However, for every success, including Frick,

Vilter, York, Sabroe, Halls and Sulzer, there were many

more who failed to survive.

Lack of appropriate machines, materials and manufac-

turing techniques was another brake on progress. In some

cases, developments in related fields such as the construc-

tion of steam engines and internal combustion engines

provided the technical insight required to move refrigeration

technology forwards. Thaddeus Lowe seems to have been

successful in manufacturing ice with a closed cycle carbon

dioxide circuit in 1867, but he neither developed the system

further, nor licensed his technology to others, perhaps

because the pressures required were too great for the

available machinery. Fifteen years later carbon dioxide was

‘rediscovered’ by Raydt (1881), Linde (1882) and Wind-

hausen (1886). The development work of J&E Hall, using a

Windhausen machine as the basis, finally established carbon

dioxide as a viable technology from 1887 onwards.

Sometimes new techniques had to be developed for the

burgeoning refrigeration industry, for example the electric

welding of brine pipes, which was pioneered by J&E Hall in

1890 for their carbon dioxide installation on SS Highland

Chief.

Lack of scientific data must also have been a handicap.

Given the lack of understanding of thermodynamics and the

lack of physical information, it is remarkable that any

progress at all was made. This is a tribute to the powers of

observation and meticulous experimental practices of these

early pioneers, who designed and constructed working

systems without any hard information on refrigerant

properties. The full thermo-physical properties of carbon

dioxide were not in fact issued until Rudolf Plank’s tables

were published in 1929.

6. The decline and fall of carbon dioxide

Carbon dioxide gained favour as a refrigerant for the

marine market in the 1880s because it was substantially

more efficient than the open-circuit air cycle systems used

up until then, and it was also more reliable. Raydt’s 1884

British Patent (number 15,475 in the name of H Lake [5])

and Windhausen’s of 1886 (number 2864 [14]) list several

advantages of ‘liquid carbonic acid’, including being

‘already much cheaper than nearly all chemicals used as

yet in ice-machines’, and being ‘a much more intense

vehicle of cold than the gases heretofore used’. It was also

stated that ‘cold, of almost any low degree, can be

produced’, and ‘in case of leakage, no more or less

unpleasant gases which are deleterious to health enter the

work-room’. Contemporary accounts of the trials of these

early carbon dioxide systems report ‘unparalleled’ quality

levels for cargoes, together with coal consumption only one-

fifth that required for an equivalent size of air cycle

machine. Open air systems relied on fans to circulate air

around the hold and this could lead to warm spots within the

cargo, but the carbon dioxide system used brine grids on the

walls to provide exceptionally even temperatures through-

out. Although more expensive to construct, the system was

cheaper to run, and quickly dominated the marine market.

However, this ascendancy was restricted to marine systems,

where ammonia was generally not acceptable. For land-

based systems an ammonia plant for brine chilling or ice

making could be constructed more cheaply but run more

efficiently. Prime movers were usually steam engines, so

low efficiency translated into high coal consumption, which

was immediately evident to plant owners. At this time heat

rejection was usually to sea water or river water, so in

temperate climates like Britain and the northern parts of the

USA it was possible to run carbon dioxide systems sub-

critical in a traditional Rankine cycle. Water usage,

however, was as apparent as coal usage, and the introduction

of atmospheric condensers by the De La Vergne company

and L Sterne&Company in the 1880s was quickly followed

by many other ammonia installers. This development, a

large, open-air pipe grid sprayed with water, acted as a

natural circulation evaporative condenser. It greatly reduced

water consumption and allowed plants to be built further

away from river or lake water. Condensing temperatures

tended to be a bit higher, and either ruled out carbon dioxide

completely, or made it much less efficient, as the latent heat

available close to the critical point reduced significantly.

Ships continued to use carbon dioxide because it was safer,

and provided the sea water temperature was below 20 8C it

was reasonably effective, but even proponents of the carbon

dioxide systems had to introduce ammonia plant to their

product range. By 1910 J&E Hall had been established as

the pre-eminent marine refrigeration builder in the world for

20 years, but felt compelled to introduce a range of ammonia

compressors to satisfy the home market for cold storage,

brewing, ice making and skating rinks.


As the 20th century progressed and manufacturing

standards improved, ammonia’s safety record also began

to improve. Pressure relief valves for ammonia plant were

introduced in the New York city safety code in 1915, and

other authorities quickly followed suit. Improved welding,

the use of electric motors instead of steam engines and the

introduction of smaller, faster running compressors all made

ammonia more feasible for carbon dioxide’s traditional core

market on board ship. Several innovations attempted to stem

the tide. The Haslam company patented a novel economiser

system for carbon dioxide reciprocating compressors in

1923 [3] in an attempt to match the efficiency of ammonia

systems as condensing temperatures tended towards the

critical point (Fig. 2).

In 1932 the Frick Company, in response to ongoing

safety concerns about large ammonia charges, started

installing a hybrid system which used carbon dioxide for

the low temperature stage, with a much smaller ammonia

plant providing the necessary refrigeration to condense the

carbon dioxide at moderate temperatures and pressures [4].

What Frick called the ‘split-stage’ system, shown in Fig. 3

was identical in principle to the modern carbon dioxide/

ammonia cascade systems which have been reported over

the last 10 years or so. Even in 1932, however, this concept

was already 65 years old, having been first proposed by

Tellier in 1867 [12], as a method of casting calcium

carbonate replicas of lifesized marble statues. It would

Fig. 2. Haslam’s Patent

appear that, in Tellier’s time, cascade systems were deemed

to be too complex, and plants were not required to operate at

the low temperatures now demanded of industrial freezers.

By the 1930s when Kitzmiller designed Frick’s ‘split-stage’

system, the lower temperatures were necessary, but most

operators seemed to be willing to accept the hazards

associated with running a large ammonia plant, so there was

no need to go to the extra expense of installing a cascade

heat exchanger.

Neither Haslam’s economiser, nor Frick’s cascade was

able to reverse the movement away from carbon dioxide in

industrial systems. Even at sea, ammonia plant was

preferred for its higher efficiency under tropical conditions.

From 1930 until the 1950s industrial refrigeration did not

really see any startling developments. The major thrust of

refrigeration research was the proliferation of refrigerators

for the domestic and light commercial market. New

synthetic refrigerants—the chlorofluorocarbons—had been

produced as a result of a specific, market-driven research

program led by General Motors and DuPont. The major

battle for technical supremacy was between GM’s vapour

compression refrigerators and Electrolux’s absorption

systems, and the weight of research funding behind GM’s

program won the day conclusively. Having produced the

fluids, it was then necessary to develop suitable compres-

sors, condensers, controls and evaporators to exploit CFC’s

potential to the full. Small hermetic compressors for

liquid pre-cooler.

Fig. 3. Frick’s ‘split-stage’ ammonia/carbon dioxide system.


refrigerators and air-conditioners provided the means to

achieve this, and once they were established the focus

returned to the industrial sector. First R12, then R22, then

R502 were introduced to industrial systems over the period

from 1950 to 1970, almost completely supplanting carbon

dioxide in the marine market, and seriously threatening

ammonia in the land market. Here was a family of chemicals

able to provide the efficiency and flexibility of ammonia

with the safety and reliability of carbon dioxide. In parallel,

new compressors running at previously unknown speeds of

up to 600, 800 and even 1000 rpm were developed, making

plants smaller, lighter, cheaper and easier to maintain—

although not necessarily more efficient. The proliferation of

Fig. 4. Presentations about CO2 at II

cheap electricity had shifted the emphasis in plant design

well away from efficiency by this time, and it could be

argued that it has not yet returned.

7. Reappraisal

The rapid decline of CFC systems in the late 20th

century has resulted in a tremendous increase in refriger-

ation research, as ‘new’ alternatives are sought. This search

has included a return to some old techniques including

ammonia and carbon dioxide. Carbon dioxide was identified

as a practicable option for various refrigeration cycles in

R conferences and congresses.


several areas almost simultaneously. In 1990 Prof Gustav

Lorentzen published a patent application for a trans-critical

carbon dioxide system for automotive air-conditioning [6].

In 1991 Dr Forbes Pearson submitted patents in Britain,

France, Germany and the USA on the use of carbon dioxide

as a volatile secondary refrigerant, including a novel hot gas

defrost system [10]. At much the same time, Stal AB

developed the use of carbon dioxide as a volatile secondary

refrigerant in supermarket systems for the Swedish market,

and the Liquid Carbonic Corporation published patents in

Spain and the USA covering a configuration similar to the

Frick ‘split-stage’ system of 1932, applied to spiral freezers.

This seems like a rapid rediscovery, but most of the research

effort applied to this topic to date has in fact been in the

commercial, air conditioning, automotive and heat pump

markets. Until recently, the industrial sector, which was the

only market for carbon dioxide systems in the 19th century,

has been somewhat neglected. In 1994 Prof Lorentzen

inaugurated the series of IIR conferences which now bear

his name, on ‘New Applications of Natural Working Fluids

in Refrigeration and Air-Conditioning’. Fig. 4 shows the

number of CO2 papers presented at these conferences and at

the IIR’s Congresses since then. The figures above each

column are the percentage of the total number of papers at

that conference that were related to carbon dioxide.

Lorentzen’s address to the first conference was also

summarised in an article in the International Journal of

Refrigeration [7] which covered all major sectors of the

refrigeration market.

It can be seen that, within the Gustav Lorentzen

conferences from 1994 to 2004 the number of papers on

carbon dioxide in one form or another has risen from six to

50, and the proportion of the total conference has risen from

7 to 48%. Likewise at the Congress in the Hague in 1995

there was only one paper on carbon dioxide out of four

hundred, but in Sydney in 1999 there were 16 (3.5%). In

Washington, DC in 2003 there were 31 papers (7.2%).

However, although this increase is dramatic, it has been

concentrated on the commercial and air conditioning

markets. From all these conferences there are only 10

papers specifically on industrial topics out of nearly 200 on

carbon dioxide.

In response to this lack of development in the industrial

field a group of European contractors, end-users, academics

and manufacturers formed an ‘interest group’—a forum for

the exchange of ideas, experiences and needs. The carbon

dioxide interest group (c-dig) met for the first time in

Switzerland in July 2000 with nine organisations rep-

resented. Initially the group was structured to avoid

commercial conflict, but it quickly became apparent that

information should be disseminated as widely as possible to

encourage installations in as many countries and market

segments as possible. To date the group has met on 12

occasions, and is now structured on more formal lines.

Topics investigated have included the testing of compres-

sors and lubricants, evaluation of cascade performance,

investigation of trans-critical systems, heat exchanger

design and oil separator design. Related topics have

included the physiology of carbon dioxide and the effects

of water in CO2 systems. These presentations have been

extremely useful in generating a rapid field development,

but they have been of a pragmatic, practical nature, and in

general they have not been written up for presentation in a

more formal academic context. During this time several

industrial carbon dioxide systems have been commissioned,

and site visits have been conducted for c-dig by members.

These have included a visit to a Swiss ice rink in Bern,

converted by W Wettstein AG from ammonia to carbon

dioxide, a visit to the coffee freeze drying plant installed by

Star Refrigeration for Nestle at Hayes, and visits to various

Dutch installations by York and Bort de Graaf. Meetings

have also been held at the laboratories of DTI in Aarhus,

Denmark, TNO in Apeldoorn, The Netherlands, TU-

Dresden and ACRC in Urbana-Champaign. At the same

time, other companies, mainly also in Europe, have also

been applying carbon dioxide to industrial systems. These

experiences have shown carbon dioxide to be eminently

suited to the requirements of modern industrial systems,

whether used as the low temperature fluid in a cascade

system, as an evaporating secondary refrigerant or as the

refrigerant in a transcritical plant.

8. Future possibilities

The limiting factor for most carbon dioxide systems is

currently pressure. This does not appear to be a long-term

impediment, and compressors, pumps, valves and controls

are already on the market suited to operation at 40 bar g.

This is sufficient for cascade operation with an intermediate

temperature of about 0 8C, but it is not quite high enough to

enable an effective hot gas defrost to be engineered. The key

development required in the near future for industrial

systems is therefore compressors capable of operation at

50 bar g. for cascades, or 100 bar g. for trans-critical

systems. The latter have not yet been applied to industrial

applications, but this may follow, provided compressors are

available, and appropriate control devices can be devised.

These systems will be particularly appropriate where there

is a need for high-grade heat recovery. The use of

economised circuits will also gain importance as cascade

system intermediate pressures increase since the percentage

benefit of economising increases as the critical temperature

is approached. These developments in the industrial field

need not only apply to very large systems. As compressor

development continues and smaller machines become

available, it will be possible to engineer packaged cascade

plant comprising a semihermetic carbon dioxide compressor

of, say 50 kW capacity with a suitable ammonia or propane

compressor, perhaps also semihermetic, using brazed plate,

plate and shell or microchannel heat exchangers to give a

low charge, virtually leak-proof, compact installation using


only ‘natural’ refrigerants. The system could be arranged to

provide reverse cycle defrosting of low temperature CO2

evaporators, making it eminently suitable for small freezers

and low temperature cold stores. Efficiencies for this system,

should be at least as good as for economised single-stage

ammonia plant, and better than a typical HFC installation of

this size, and capital cost will depend primarily on the unit

cost of the components. This, in turn, will be primarily

dictated by the size of the market.

9. Conclusion

Carbon dioxide system development was driven in the

19th century by the shortcomings of the alternatives; air

cycle, ether, absorption and ammonia. It was impeded by

lack of knowledge, lack of commercial awareness, lack of

manufacturing capability and lack of concern for safety.

Carbon dioxide was probably the cheapest available

refrigerant. One system patent even describes it as a by-

product of the production of calcium chloride, used as the

brine for the ice-maker. In the 21st century it is no longer

necessary to make your own brine or carbon dioxide.

However, many of the drivers for development—short-

comings in the alternatives—have come to the fore again.

This time round, manufacturing is easily able to cope with

the requirements, and an increased level of safety awareness

backed by appropriate international codes and legislation

will help to make carbon dioxide a preferred choice for

industrial systems in the near future.

References

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Frankfurt, 1994. p. 134.

[3] A.S. Haslam, Improvements in compression refrigerating

apparatus, British Patent No. 165929; 1921.

[4] F. Kitzmiller, CO2 split stage, Power (1932) (19 January 1932).

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manufacture of ice, British Patent No. 15,475, London; 1884.

[6] G. Lorentzen, Trans-critical vapour compression cycle device

Patent No. WO/07683; 1990.

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[12] C. Tellier, L’ammoniaque dans l’industrie, Paris; 1867: p.

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[13] R. Thevenot, A History of Refrigeration, IIF/IIR, Paris; 1979.

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[15] W.R. Woolrich, The men who created cold: a history of

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carbon dioxide—new uses for an old refrigerant

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